In order to ground your mast you will need to drill a hole in your mast and attach a 1/0 Marine batery type cable to it and pull the boat out of the water and mount a grounding block on the outside of the hull below the waterline. DO NOT use one of the blocks that is instended for a ground for SSB''s. A lightning strike would blow that plate right off the hull. You are almost better off leaving the mast "isolated" because if you integrate the mast grounding with your boats grounding system you may end up blowing your thruhulls or propshaft out of the boat in the event of a strike.
You might want to consult Nigel Calders book about this, or Don Casey''s book on Sailboat Electrics.